Pumping device



R. L. HIRSCH May 13, 1969 PUMPING DEVICE Sheet a Q. w a; 3 8 m 6 5 M Q QMa 2 8 Z 2 V 0 b 2 r 8 a n u M a M/, II" 3 Hvl li i IN I I I l I I I IIlka I: Cfilll Lu|+ 4 M w W w o, w 4 2|L v a 2 m R. L. HIRSCH May 13,1969 PUMPING DEVICE Sheet Filed June 9, 1967 Pic-3.4 96

INVEN Tore. RosERT LHmscH, BY Hood u -i- M ATTORNEY- United StatesPatent "ice 3,443,742 PUMPING DEVICE Robert L. Hirsch, Fort Wayne, Ind.,assignor to International Telephone and Telegraph Corporation, Nutley,N.J., a corporation of Maryland Filed June 9, 1967, Ser. No. 644,896Int. Cl. F04b 37/02 U.S. Cl. 230-69 7 Claims ABSTRACT OF THE DISCLOSUREA pumping device comprising a chamber from which gases are to beremoved, a collector surface disposed in said chamber for receivinggases, the gases being chemically combined with said surface to providea reaction product thereon, and means for removing the reaction product,thereby permitting additional reaction product to form. In a preferredembodiment of the present invention, a wire-like brush is utilized toremove the reaction product.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates generally to pumping devices, and more particularly to pumpingdevices which may be used to eliminate gases in a high-vacuum system. Ahigh-vacuum system is one which is maintained at, say, from 10" torr to10- torr. The pump of the present invention is not intended for use inpressures greater than 10- torr.

Description of the prior art Several different types of pumping deviceswhich are intended to maintain or improve the vacuum in a highvacuumsystem have been developed in the past several years. Probably, the mostcommon of these types is a diffusion pump. The operation of ordinarymercury or oil diffusion pumps consists of heating the pumping fluiduntil a sufiicient quantity of vapor is obtained. This vapor rises tothe top of the reservoir and into a jet assembly. Upon flowing out ofthe jet assembly, the pump fluid molecules entrap molecules of the gasto be pumped and force them into a region where they can be removed by aforepump. The cycle is repeated continuously until almost all of thevapor is removed. One of the main disadvantages of such a diffusion-typepumping system is that the process necessarily involves the use ofvapors which are in some instances undesirable. Where an oil-typediffusion pump is used, the pump is a source of organic vapors whichwill coat the walls of the vacuum chamber and any parts therein.Mercury-type diffusion pumps require elaborate liquid air-cooled trapsto prevent mercury vapor from entering the system to be evacuated.

Another type of vacuum pump is generally referred to as an ion pump. Inthis type of pump, there is generally located within the evacuatingenvelope an electron source and at least one ion collector element. Theelectrons are oscillated in the path of gas molecules moving within theenvelope, the gas molecules being bombarded by the electrons. Thiselectron bombardment results in ionization of the molecules, which ionsare attracted to a cathode in which they are embedded. Further burial isaccomplished by sputtering from the cathode to produce finely dividedmetal which aids the vacuum process through chemical reaction,absorption, and burial. Titanium is generally selected as a suitablemetal for this application by reason of its relatively high chemicalactivity, especially insofar as the more usual gases (vapors) areconcerned, and by reason of the stability of the majority of thetitanium compounds in the solid form thereof 3,443,742 Patented May 13,1969 at ordinary temperature. It will be apparent, therefore, that anion pump requires a complicated structure comprising an electron source,means for oscillating the electrons and a cathode.

In still another type of pump, titanium is continually deposited oncollector surfaces to react chemically with vapors in the regionthereof. Some disadvantages of such a system, which usually operates onthe principle of sublimation of titanium from a filament or anode ontothe adjacent casing walls, are the temperatures required for titaniumsublimation, the limited amount of titanium that can be depositedwithout recharging the source, and the fact that the casing walls mustbe maintained at room temperature or below in order to achieve a highgettering rate. Thus, the high temperature of the source and the lowtemperature of the walls represent conflicting conditions.

SUMMARY OF THE INVENTION The pumping device of the present inventioncomprises a pump chamber or envelope from which gases are to be removed,the pump chamber or envelope being in communication with a main vacuumchamber. Thus, by evacuating the pump chamber, the main chamber isevacuated. Of course, the main chamber is evacuated to pressures of,say, 10- torr by conventional pumping means capable of achieving suchpressures. The pump chamber is constructed with a suitable surface forreceiving gases, the gases being chemically combined with the collectorsurface to provide a reaction product thereon. As the gases combine withthe collector surface, the pressure in the pump chamber necessarilydecreases and, consequently, additional gases move from the main chamberto the pump chamber. By providing means for continually removing thereaction product from the collector surface, these additional gases willcontinue to combine chemically with the fresh collector surface.

In a preferred embodiment of the present invention, the pump chamber iscylindrically-shaped and the collector surface comprises a cylindricalwall of titanium which is concentrically mounted in the pump chamber.The collector surface may be the inner wall of the pump chamber. A wirebrush is engaged with the inside surface of the titanium wall, the brushbeing effective, when moved while engaged with the inside surface, toremove the reaction product therefrom so that additional reactionproduct may form.

Thus, it will be apparent that the pumping device of the presentinvention does not suffer from the aforementioned disadvantages, i.e.,the titanium does not have to be heated; the titanium wall may be madearbitrarily thick so the supply of titanium, for all practical purposes,is limitless; undesirable oil or mercury vapors are not involved; and acomplicated structure is not required. In fact. a simple rotating shaftmechanism or the like for moving the wire brush is all that is required.

It is an object of the present invention, therefore, to provide apumping device which does not utilize contaminating vapors or hightemperatures to pump gases.

Another object of the present invention is to provide a pumping devicefor a high-vacuum system, Which device comprises a collector surface forreceiving gases, the gases being chemically combined with the collectorsurface to form a reaction product thereon, and a means for removing thereaction product so more reaction product can be formed.

Still another object of the present invention is to provide such adevice wherein the means for removing the reaction product comprises awire brush or suitable scraper which is engaged with the collectorsurface and means for moving the wire brush while it is engaged with thecollector surface.

3 BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and otherfeatures and objects of this invention and the manner of attaining themwill become more apparent and the invention itself will be bestunderstood by reference to the following description of an embodiment ofthe invention taken in conjunction with the following drawings wherein:

FIG. 1 is a vertical sectional view of a preferred embodiment of thepresent invention showing a cylindrical titanium wall, a wire brushengaged with the wall and means for moving the brush relative to thewall;

FIG. 2 is a cross-sectional view taken from FIG. 1 generally along theline 2-2;

FIG. 3 is a fragmentary, axial section of another embodiment of thisinvention; and

FIG. 4 is a cross-section taken substantially on section line 44 of FIG.3.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, itwill be seen that the pumping device, indicated generally by referencenumber 10, comprises a cylindrically-shaped housing having acylindrical, outer wall 12, an upper end plate 14 and a lower end plate16, the housing, therefore, defining a chamber from which vapors are tobe removed. The upper end plate 14, which is welded to the upper edge ofthe cylindrical wall 12, as indicated by reference number 18, isprovided with a centrally-located opening in which a cylindrical pipe 22is disposed. Of course, the pipe 22 is welded or otherwise securelyjoined to the end plate 14 so that gases cannot enter the pump 10 exceptthrough the pipe 22. For instance, pipe 22, which preferably has anouter diameter substantially equal to the internal diameter of the hole20, may be welded to the end plate 14 as indicated by reference number24.

The end plate 16 is welded to the cylindrical wall 12 as indicated byreference number 26 so gas cannot enter the pump 10 through the jointbetween the cylindrical wall 12 and the end plate 16. An inverted,generally bellshaped housing 28, fragmentarily shown in FIG. 1, ismounted on the underneath side of the end plate 16 by means such asscrews 30 which extend through holes 34 in a horizontal flange 32 of thehousing 28 and which are threaded into the end plate 16. A conventionalO-ring or copper gasket seal 36 is provided between the underneath sideof the end plate 16 and the flange 32 of the housing 28.

In recapitulation, it can be seen that the cylindrical Wall 12, endplate 14, end plate 16 and housing 28 define a chamber having an inputport (pipe 22) and no exhaust ports. Thus, gas entering the pumpingdevice 10 must enter through pipe 22. The pipe 22, therefore, will beconnected to a vacuum chamber, not shown, which is to be evacuated. Asstated previously, the vacuum chamber, to which pipe 22 is connected,will be preliminarily evacuated down to 10- torr or less before pump 10will be energized.

A shaft 38 is journalled in the pump 10, the axis of the shaft 38 beingsubstantially coincident with the axis of the cylindrical wall 12.Specifically, the shaft 38 is supported on at least one thrust bearing,such as thrust bearing 40 in FIG. 1 which is shown supported on abearing mount 42 which, in turn, is supported on a shoulder 44 in thehousing 28. A pair of snap rings 46 is disposed in spaced-apart grooves48 in the shaft 38 to retain the inner race of bearing 40 against axialmovement on the shaft 38.

Rigidly mounted on the lower end of shaft 38 and within the housing 28is a cylindrically-shaped iron block 50, the axis of block 50 preferablycoinciding with the axis of shaft 38. A rotatable magnet 52,fragmentarily shown in FIG. 1, is disposed outside housing 28, themagnet 52 being journalled for rotation about the axis of shaft 38. Whenthe magnet 52 is rotated, block 50 is rotated, and, since block 50 isrigidly mounted on shaft 38, shaft 38 is rotated. Thus, the rotatablemagnet and iron block 50 comprise means for driving shaft 38, thedriving means being arranged so shaft 38 can be rotated without breakingthe seal of the pumping device 10 chamber. Such means for driving ashaft are well known and need not be discussed in detail in thisdescription.

The pumping device 10 is not limited to the driving means illustrated inFIG. 1 and several other types of driving means may be developed andused by those persons skilled in the art, the only requirement beingthat rotation of the shaft 38 does not permit vapors and gases to enterthe pumping device 10 chamber.

The pumping device 10 further comprises an inner wall 56 which in theillustrative embodiment is a cylindrical wall having an outer diametersubstantially equal to the inner diameter of the cylindrical wall 12.Referring to FIG. 1, it will be seen that end plate 14 is provided witha circumferentially extending notch 58 for receiving the upper edgeportion 60 of the inner wall 56 and that the lower edge portion 62 ofthe inner wall 56 is held outwardly against cylindrical wall 12 by aring 64. Ring 64 is held in a selected vertical position by means suchas the crew 66 shown in FIG. 1.

An axially extending brush or scraper, indicated generally by referencenumber 68, is engaged with the inside surface of the inner wall 56, thebrush 68 comprising a rigid holder 70 and a scraper portion 72 which maybe constructed of stiff, wire-like material. The scraper portion 72 mayalso be a single flexible blade or blades arranged to engage and scrapethe inside surface of inner wall 56.

As seen in FIG. 1, means are provided for drivingly connecting holder 70to shaft 38 so that, when the shaft is rotated, scraper portion 72 ismoved about the inside surface of inner wall 56. Specifically, anadapter 74 is mounted on the upper end of shaft 38 and held againstrotation relative to the shaft by means of screws 76. A pair of links 78is provided for connecting holder portion 70 to the adapter 74, each ofthe links 78 being pivotally connected to the holder portion 70 asindicated at 80 and pivotally connected to adapter 74 by one of thescrews 76. Thus, when the pivot point 80 moves about the axis of screws76 in the direction of arrow 82, holder 70 is moved radially outwardlytoward the inside surface of inner wall 56. A horizontally disposed ring84 is slidably carried on adapter 74 as shown in FIG. 1. A collar 86 isarranged to fit over the upper end of shaft 38 and to rest on ring 84which is held against downward movement by links 78. The collar 86 isprovided with an axially extending hole 88 through which a screw 90extends, the screw 90 being threadedly engaged with adapter 74 asindicated at 92. Thus, by tightening screw 90, the ring 84 is urgeddownwardly against links 78 to urge the scraper portion 72 intoengagement with the inside surface of inner wall 56.

An annular cup 94 is mounted on shaft 38 by means such as the screw 96,the annular cup 94 being arranged to collect reaction product which isbrushed or scraped from the inside surface of wall 56 and which fallsdownwardly toward cup 94. It will be seen that ring 64 acts as ashoulder or deflector causing the reaction product to fall into cup 94.

In a preferred embodiment of the present invention, inner wall 56 isfabricated from titanium and the balance of the parts which are exposedto the inside of the pumping device 10 except the iron block 50iarefabricated from stainless steel. Thus, in a preferred embodiment of thepresent invention, the brush 68 has stainless steel bristles engagingthe inside surface of wall 56.

It will be apparent that the inner wall 56 may be removed from thepumping device 10 by removing housing 28, shaft 38 which carries brush68, annular cup 94 and ring 64 which secures inner wall 56 to the outerwall 12. The inner wall 56 is therefore an easily replaceable element ofthe pumping device 10.

In operation, pumping device receives gas molecules through the pipe 22,the gas molecules being collected on the inside surface of inner wall56. Since, in a preferred embodiment, inner wall 56 is fabricated from amaterial such as titanium, the gas molecules combine chemically with thesurface of inner wall 56 to form a reaction product, such as titaniumoxide, thereon. After a period of time, the inside surface of inner wall56 will be entirely covered with this reaction product and consequentlythe gas molecules cannot be gettered. This invention, therefore,provides means for continually removing the reaction product soadditional reaction product can be formed. Obviously, the gas moleculeswhich chemically combine with the inside surface of inner wall 56 areremoved from the system and therefore the pressure in the system isdecreased. Generally speaking, the pumping device 10 comprises means forproviding, in a high-vacuum system, a large surface of reactive metal,such as titanium, which is continually scraped and cleaned so that gasmolecules can be continually gettered thereby.

Titanium will readily combine with hydrogen, nitrogen, oxygen, carbonmonoxide, carbon dioxide and water vapor. Of course, in some instances,barium may be used to provide a collector surface since barium willreadily combine with oxygen and compounds thereof to form stable, lowvapor pressure compounds.

It will be apparent that pumping device 10 is controllable in that thescrew 90 can be adjusted to determine the pressure with which brush 68is engaged with inner wall 56. Of course, a coiled, compression springmay be disposed between collar 86 and ring 84 to urge the ring 84downwardly against the links 78, thereby resiliently engaging brush 68with the inside surface of the inner wall 56.

The pumping device 10, as illustrated, is used in the verticalarrangement illustrated so that reaction product removed from the insidesurface of wall 56 can fall down into the annular cup 94. For use in thehorizontal position or any position therebetween, a slot in the cylindercan be provided to catch the reaction products.

It will be apparent that the pumping device of the present invention isnot limited to the cylindrical arrangement shown in FIGS. 1 and 2 andthat one skilled in the art, using the concepts of the presentinvention, could easily devise a system which would have a flatcollector surface and some other means for moving the brush 68 againstthe flat surface.

Referring to FIGS. 3 and 4, a second embodiment of this invention willbe described. Like numerals indicate like parts. In this embodiment, thecylindrical housing 12 has positioned thereinside a titanium cylinder56a in spaced coaxial relationship. The titanium cylinder 56a is mountedon the housing 12 by a series of helical springs 96 circumferentiallyand axially spaced as shown. The springs 96 are under compression andare secured at the inner ends thereof to attachment rings 97 secured tothe cylinder 56a. The opposite ends of the springs 96 are frictionallyengaged with the housing 12 under a force dependent upon the degree ofcompression of the springs, the force being adequate to hold thetitanium cylinder 56a in position. By means of this spring mounting, thetitanium cylinder 56a is capable of being moved radially with respect tothe housing 12.

Coaxially positioned inside the titanium cylinder 56a is the rotatableshaft 38 having mounted thereon a rigid brush holder 98. This brushholder 98 is formed of two fiat pieces 104 and 106 abutted together andclamped to shaft 38 by means of suitable screws 100. A square cutout 102formed between the two fiat pieces firmly frictionally embraces theshaft 38 such that rotation of shaft 38 will result in rotation of thebrush holder 98. The brush 72 is also clamped between the two flatpieces 104 and 106 and engages the inside surface of the titaniumcylinder 56a the same as explained in connection with the precedingembodiment.

A guide ring 108 is secured to the housing 12 in coaxial relationtherewith and extends radially inwardly to a position just beneath thetitanium cylinder 56a as shown. The internal diameter of the ring 108 isabout equal to that of the titanium cylinder 56a.

The upper end wall of chamber 12 as well as the ring support serve asend stops or guides for the titanium cylinder 56a in limiting verticalmovement thereof. Preferably, the length of the titanium cylinder 56a ismade only slightly smaller than the distance between the end wall andring guide 108.

A residue cup 94 is secured to the shaft 38 for rotation therewith andis disposed immediately beneath the titanium cylinder 56a to catch theresidue which falls from the inner surface of the titanium cylinder 56a.

Operation of this embodiment of FIGS. 3 and 4 is substantially identicalto that of the arrangement of FIGS. 1 and 2. However, in the initialassembly, the bristles of the brush 72 are engaged forcefully with theinside surface of the titanium cylinder 56a, the bristles forming thisbrush 72 being sufiiciently resilient to engage forcefully this surface.Thus, as the shaft 38 is rotated, the brush 72 will rotate and perform ascraping action against the cylinder surface. Inasmuch as the cylinder56a is spring-mounted, it is free to flex radially. If there should beany eccentricities between the shaft 38 or the brush 72, these areautomatically compensated for by reason of the radial movement ofcylinder 56a. Additional advantages reside in the construction of thebrush assembly and its mounting on the shaft 38 being simpler. Also, thespring mounting of cylinder 56a results in a decrease in vibration andnoise.

A third embodiment is illustrated also in FIGS. 3 and 4 in the respectthat the cylinder 56a may be provided with an axially extending slot 110such that the pump may be operated on its side with the residue from theinside of the cylinder 56a falling therethrough as the brush 72operates. For such operation, obviously the residue cup 94 would not beneeded.

While there have been discussed above the principles of this inventionin connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation to the scope of the invention.

What is claimed is:

1. A pumping device comprising a cylindrically-sh-aped housing defininga chamber from which gases are to be removed, the inside surface of thecylindrical wall of said chamber being formed of a material which willchemically react with the gases to form a reaction product on saidsurface, and means for removing said reaction product from said surface,said removing means comprising elongated axially extending scraper meansengageable with said inside surface and effective when moved whileengaged with said surface to remove said reaction product, a shaftjournalled for rotation inside said chamber, the axis of said shaftsubstantially coinciding with the axis of said chamber, means fordrivingly connecting said sgraper means to said shaft, and means forrotating said s a t.

2. A pumping device as in claim 1 wherein said material from which saidinside surface is formed is titanium and wherein said scraper meansincludes Wire-like bristles which are engaged with said surface.

3. A pumping device as in claim 1 wherein said means for drivinglyconnecting said scraper means to said shaft includes at least one linkhaving one of its ends pivotally connected to said scraper means and theother of its ends pivotally connected to said shaft, said link extendingradially outwardly from said shaft, and means for pivoting said link onsaid shaft to urge said scraper means into engagement with said surface.

4. A pumping device as in claim 1 further comprising an annular cupcarried by said shaft and arranged to receive the reaction productremoved from said surface,

the axes of said shaft and cylindrical Wall being vertical.

5. A pumping device comprising a cylindrical housing defining a chamberfrom which gases are to be removed, a collector surface disposed insidesaid housing for receiv ing gases, the gases being chemically combinedwith said collector surface to form a reaction product thereon, meansfor removing said reaction product from said surface thereby permittingadditional reaction product to form, said removing means comprising ascraper engaged with said surface and means for moving said scraperrelative to said surface, said collector surface being the inner surfaceof a cylindrically shaped titanium wall, said wall being substantiallycoaxially positioned inside said housing, and means for resilientlymounting said titanium wall inside said housing whereby said wall iscapable of moving radially.

6. A pumping device as in claim 5 wherein said resilient mounting meansincludes a series of springs interposed between said wall and saidhousing.

7. A pumping device as in claim 5 wherein said titanium wall has anopening therein through which residue scraped off the surface thereofmay fall.

References Cited UNITED STATES PATENTS 2,957,619 10/1960 Haine et a1.230--69 3,107,044 10/1963 Brubaker et al 23069 ROBERT M. WALKER, PrimaryExaminer.

